Use of Study Area Resources:
Migration and growth of elvers/juveniles (adult American eels spawn in the
'Sargasso Sea', in the mid-Atlantic Ocean). American eels are found
from Greenland southward to the east coast of South America (Atlantic States
Marine Fisheries Commission 2000).

Habitat Requirements:
American eels have "multiple habitat requirements, utilizing open oceans,
large coastal tributaries, small freshwater streams, lakes and ponds" (Atlantic
States Marine Fisheries Commission 2000). Eggs hatch at sea. The
larval stage (leptocephalus) lasts about a year, during which time they are
transported along the eastern coast of the U.S. by the Antilles Current,
Florida Current, and eventually the Gulf Stream. Gradually the leptocephalus
develops into an eel-shaped juvenile form, of which the initial unpigmented
stage is known as the glass eel. As these reach a length of 6-9 cm they turn
brown and are known as elvers. Elvers actively migrate toward estuaries and
freshwater in the spring, most moving up rivers and streams over a period
of months or even years. (Ross 1991) They can survive out of water so long
as their skin is moist, and this may contribute to their ability to surmount
stream obstructions including dams and falls that block migration of other
species (Bigelow and Schroeder 1953, Ross 1991). Because of their small size,
elvers are unable to ascend fish ladders designed for adult anadromous species;
they will attempt to scale wet surfaces include dam faces and wet rocks (Atlantic
States Marine Fisheries Commission 2000). Some elvers also reside in
coastal embayments and nearshore areas. (Atlantic States Marine Fisheries
Commission 2000).

As elvers grow, they enter a sub-adult stage known as yellow eels. Growth
towards maturation occurs over a period of 6-7 years in the Chesapeake region
(Hedgepeth 1983 in Atlantic States Marine Fisheries Commission 2000), and
is believed to occur more slowly in colder northern waters. During this time
yellow eels are bottom dwellers, feeding opportunistically on whatever food
is available, living or dead, including frogs, crustaceans, insects, worms,
shellfish, and small fish (Bigelow & Schroeder 1953, Ross 1991). Eels
are primarily nocturnal foragers, returning to specific resting areas by
day, or burrowing into soft mud leaving only their heads protruding (Ross
1991, Fahey 1978 in Atlantic States Marine Fisheries Commission 2000). The
skin color of yellow eels varies widely, depending on the substrate, and
can lighten or darken over a period of hours if they are moved to a different
bottom. Typically they are muddy brown or olive brown above, with yellow-brown
sides, and a yellowish-white belly. Females grow to larger sizes than males,
reaching lengths from 2 to 4 feet. (Bigelow and Schneider 1953). Important
habitats for yellow eels include the soft, undisturbed sediments of river
and lake bottoms, estuaries, and large streams.

With the onset of sexual maturity, eels undergo a final metamorphosis into
the silver eel stage. During this stage, which occurs in Autumn, the skin
thickens and darkens to a metallic bronze color, the body fattens and eyes
grow more prominent. The maturing eels descend the streams by night, no longer
feeding. Migrating eels are highly capable of passing over, around and under
stream barriers. The digestive tract degenerates, and maturation of the gonads
occurs after they reach salt water. Spawning occurs midwinter in the Sargasso
Sea of the Atlantic, and death follows. (Bigelow and Schroeder 1953, Ross
1991)

Eels residing in coastal habitats may use a wide range of substrate types,
temperatures, flows, and salinity levels. They are found to be most
prevalent in the nearshore, shallow embayments and tributaries (Atlantic
States Marine Fisheries Commission 2000). Adult oceanic habitat
requirements are not known. However, American eel have been taken at depths
greater than 6000 meters (Atlantic States Marine Fisheries Commission 2000).

Habitat Mapping:Riverine and lake habitat was mapped primarily from occurrence data,
obtained from several sources. Eipper et al. (1982) mapped upstream migratory
pathways for catadromous and anadromous fishes throughout New England at
a relatively small scale. We coded the corresponding stream segments
as suitable habitat on 1:24,000 USGS digital maps (Maine, New Hampshire)
and 1:100,000 maps (Massachusetts), supplemented by 1:24,000 for minor features
absent in the 1:100,000 maps. Where eel migration pathways were not
specifically labeled, we assumed that they could use streams and ponds frequented
by other migratory species. Eipper was used for the whole study area. This
general information was considerably supplemented state by state with more
specific surveys. In Massachusetts we were supplied with point data from
Hartel et al. (in press), and from a GIS coverage developed by Massachusetts
Department of Fisheries, Wildlife and Environmental Law Enforcement
(http://www.state.ma.us/dfwele/gisprog/gisanad.htm).
In New Hampshire we added migratory pathways that New Hampshire Fish and
Game biologists informed us were used by other anadromous species. In Maine
we used Maine Department of Inland Fisheries and Wildlife unpublished stream
electro-fishing and other stream survey information and a state-wide fisheries
survey of lakes and ponds. We coded as habitat all reaches downstream of
ponds having eels. We also coded all tributaries of the Pleasant, Sheepscot,
Medomak, and East Machias river as eel habitat on the basis of observations
by Ken Oliveira (Univ. of Maine). Occurrences of catadromous or anadromous
species at a sample site were taken as indicating use of all downstream reaches.

Artifacts of grid-cell mapping of stream and riverine themes may in
some cases cause habitat omissions, and in others aquatic habitat values
in primarily upland areas. Fish habitats were gridded from continuous
polygons/arcs derived from USGS hydrology coverages. Single line arcs were
necessarily converted into strings of cells, each with a minimum width of
30 m (the cell dimensions). Even where the dominant land cover of a
cell was upland, we retained the habitat value for a stream passing through
the cell. As a result, some upland areas will display habitat value
for anadromous fishes.

The grid process left discontinuities when converting narrow (< 30 m wide)
polygon features, such as small rivers, where only part of a cell was crossed
by aquatic habitat. Moreover, where National Wetlands Inventory polygons
representing wetlands and water bodies differed from those of USGS,
the only fish habitat we retained was that which corresponded to aquatic
classes in the former. Therefore, fish habitats and migratory pathways may
not appear as continuous extents of habitat, or extend to the boundaries
of contiguous wetlands in all cases.

Coastal habitat was mapped at two levels. Inshore areas which
may serve as habitat for juveniles and adults ("harbor, stream mouth, muddy
estuary or tidal marsh" of Bigelow and Schroeder 1953), were mapped by selecting
estuarine and marine portions of the study area having unconsolidated substrates
and depths from mid-intertidal down to 60'. Deeper areas, which may
be used during migration by larvae and migrating adults were mapped
as lower value habitat.

Habitat Suitability:
Habitat suitability for this model is scored on the basis of known or apparent
use. Riverine and lake habitats delineated from known
occurrences were scored 1.0; inshore areas were scored 0.5, and areas
deeper than 60' were scored 0.2.